Three projects are in progress. The first is concerned with measurements of the streaming potential across artificial lipid bilayer membranes containing gramicidin channels. We have shown previously that this streaming potential can be interpreted in terms of the number of water molecules per channel. We are now involved in improving and extending these measurements. The second project is an attempt to measure the water permeability of the gramicidin channel as a function of the ion concentration. This should provide information about the binding constants of the ion in the channel. The last project is concerned with measurements of the diffusive permeability and reflection coefficient of the human red cell. Both stopped-flow and fast flow procedures have been developed. The primary goal of this project is to determine whether water and small solutes share the same pathway.